Iron sulfide (FeS) and hydrogen sulfide (H2S) pose serious operating, system, functional, and safety problems in several operational areas of oil & gas production, including water injection systems, oil well flowline and field process systems, oil and water storage tanks, and gas conditioning systems. H2S present in the liquid or gas phase of oil well production can cause corrosion failures and toxicity problems, as well as combining with iron to form iron sulfide, which can easily deposit in flowlines, plug equipment, plug downhole pumps, plug filters, plug injection lines and form flow blockages at the formation face and within downhole oil and gas producing reservoirs. Iron sulfide is frequently formed under normal operating conditions in oilfield equipment from the combination of iron with H2S in produced water.
FeS is a challenging problem in oilfield water systems. Several commercial methods have been available to dissolve FeS, for example, sodium hypochlorite, acids, chelating agents, etc. Each of the above methods have drawbacks. Both iron oxide and sulfur are insoluble in water and can result in formation plugging problems. Many different acids can be used to dissolve FeS, however, reaction of acids with FeS can result in the release of H2S in the atmosphere and in the injection fluid. H2S is highly undesirable because of its toxicity and, eventually, can lead to reservoir souring. Furthermore, acids lower the pH which can lead to accelerated corrosion rates in metal pipelines and fluid handling equipment.
There are certain chelating agents that demonstrate some effectiveness in converting FeS into soluble iron but only at low H2S concentrations (<5 ppm). At higher H2S concentrations in fluids, chelating agents are impeded from action. In comparison, acrolein acts on H2S and FeS through a chemical reaction with the sulfide element, producing nontoxic, soluble, low molecular weight product. Acrolein is a non-corrosive liquid and is not an oxidizing chemical. The reaction of acrolein with FeS is irreversible and permanently converts the FeS, present in the fluid produced within the oil well system, into a water-soluble product.
Acrolein (also called 2-propenal or acrylic aldehyde) is the simplest unsaturated aldehyde, having a chemical formula of C3H4O. Acrolein has a boiling point of 53° C. and a high synthetic and technical potential due to the conjugation of the carbonyl group with a vinyl group. Acrolein is a highly toxic material having a distinctive pungent odor, and a flammable material with high environmental polluting potential. Acrolein has enormous industrial applications as a significant intermediate for acrylic acid production. The largest commercial use of acrolein is an intermediate in the synthesis of acrylic acid and as a biocide. Acrolein is currently produced commercially in large quantity by the oxidation of propylene using multi-component mixed oxide catalysts. The primary source of propylene is crude oil.
The production of acrolein from glycerol has been generally known since around 1918. During the early chemical industry days, the limited availability of glycerol or the increased cost of glycerol over the cost of propylene resulted in propylene, which is produced from crude oil, serving as the primary feedstock in the chemical industry.
Acrolein is used successfully in oilfield applications both onshore and offshore for reducing the harmful effects of H2S and FeS in produced water. Acrolein treatments are very effective in both cost and performance. Several published industry papers describe how effective acrolein is in treatment of H2S and iron sulfide in oilfield applications: Kissel, Charles L. et al. (1985). SPE 11179, “Factors Contributing to the Ability of Acrolein to Scavenge Corrosive Hydrogen Sulfide.” Salma, T. et al. (2000). SPE 59708, “Cost Effective Removal of Iron Sulfide and Hydrogen Sulfide from Water using Acrolein.” Penkala, J. E. et al. (2006). SPE 98067 “Acrolein Application to Mitigate Biogenic Sulfides and Remediate Injection-Well Damage in Gas-Plant Water-Disposal System.” Horaska, D. D. et al. (2009) SPE 120238, “Field Experiences Detailing Acrolein (2-propenal) Treatment of a Produced Water Injection System in the Sultanate of Oman.”
In addition to its ability to dissolve FeS and scavenger H2S, acrolein is also a highly effective micro-biocide used commercially since about 1960 and has found wide use in oil and gas production industry. Acrolein is delivered as a liquid product typically supplied in a regulated, specialized metal container with a special control apparatus to prevent the release from transfers between tanks and injection equipment. Acrolein is difficult to handle and apply due to the toxicity it poses to its handlers and the surrounding workers.
Handling acrolein liquid can present special challenges and requirements to protect workers and the environment. Acrolein is generally delivered to the field location in a pressure tank and discharged using an inert gas. The acrolein containers are built to comply with international transportation regulations for this purpose. The activity of acrolein in treatment water is managed at a dilute concentration in water (below 2%) to safely handle the treatment and to prevent potential polymerization of the acrolein with hydrocarbons. Several handling methods of use have been plagued by the very real possibility of the rupture or leakage of the storage and feeding equipment employed, with consequent probability of toxicity to personnel or animals and/or fire-explosion damage to plants and equipment. Even if the fatal consequences of inhalation, fire or explosion are avoided, the irritation and lachrymation caused by even minute quantities of escaped vapors is a pronounced disadvantage.
Despite the many dangers of using acrolein, it provides a unique all-in-one chemical solution to assist in resolving problems associated with sulfide contamination. Acrolein is highly efficient in scavenging H2S. As a sulfide scavenger, acrolein reacts in a 2:1 molar ratio to form water soluble, irreversible sulfide containing reaction products. The reaction with H2S is rapid, whereas the reaction with FeS is slower due to the dependence on the shift from FeS to H2S and soluble iron, whereby it scavenges the H2S. Acrolein can be used for downhole treatment of production and injection wells to control FeS solids, H2S, bacteria, pump failures, and microbiological influenced corrosion (MIC). Acrolein can be useful in the treatment of oil storage tanks, settling tanks, heater treaters and free water knockouts to improve oil water separation and control bacteria. Acrolein can treat water storage air flotation units, water storage tanks, and surge tanks to control sulfide solids and bacteria. Acrolein can treat filters to control bacteria, FeS solids and improve filter run times. Acrolein can protect flow lines and water injection lines by controlling bacteria, FeS solids, MIC, H2S and under-deposit corrosion. The fact that acrolein is non-corrosive and non-surfactant in nature makes it compatible with surface and downhole equipment and oil-water separation equipment. In addition to oilfield applications of acrolein, it is used as a highly effective aquatic herbicide to control subaquatic plants in water distribution channels, and it is also used as a replacement for pest control agents used for the control of nematode infestation in agriculture.
Glycerol serves as a feedstock to produce acrolein. It is well known in the art to prepare acrolein by dehydrating glycerol. The production of acrolein in the presence of a solid catalyst, also called heterogenous catalyst, has been known for many years. The dehydration of glycerol to produce acrolein, using heterogenous catalysts in continuous flow fixed bed reactors is reported in several industry journals. For example, Herbert in U.S. Pat. No. 2,042,224 teaches the use of a novel process wherein acrolein can be prepared by thermal decomposition of anhydrous glycerol in the presence of certain strong dehydrating agents, such as alkali-metal acid sulfates, phosphorous pentoxide and the like. Howard in U.S. Pat. No. 2,558,520 teaches the use of a method for the preparation of acrolein by the dehydration of glycerol with a dehydration catalyst orthophosphoric acid, metaphosphoric acid or phosphorous pentoxide. Kissel in U.S. Pat. No. 5,081,314 teaches how dilute solutions of acrolein are produced on site and on demand by oxidizing propylene in a reactor using heterogeneous catalysts, which are mixtures of molybdenum, bismuth and tellurium oxides and which are deposited on a metal and used in a packed catalyst bed.
The hazards of handling, shipping, and storing concentrated acrolein can be reduced by diluting it with a solvent, like water. However, storage of dilute acrolein usually results in degradation of the material over time. Water hydrolyzes acrolein, producing hydrolysis products that retain little or no functionality as a sulfide scavenger or iron sulfide dissolver. Maximum levels of acrolein dissolved in water are about 19-25% depending on temperature. After a few days, these levels are reduced to only a few percent. It is generally known that a lower pH extends the life of acrolein in water. Even with the use of acid, after a few months, the acrolein concentration lowers to ineffective concentration levels.
There exists a need for a portable, self-contained system for generating a dilute solution of acrolein in sufficient quantities to satisfy on-demand and on-site requirements, while avoiding the problems arising from safety concerns and the handling of concentrated acrolein.
There exists a need for a system which avoids the use of solid, heterogenous catalyst or a packed catalyst bed, thus reducing the need to regenerate solid catalyst to remove fouling carbon deposits from the surface of solid catalyst. The deactivation, carbonization or coking, remains the main obstacle in the way of transportable and large-scale industrial applications.
There exists a need for a system which utilizes a renewable glycerol feedstock in the production method. Worldwide glycerol production is increasing due to the expansion of bio-diesel production, based upon triglycerides, and has led to a large surplus of its major byproduct glycerol. Glycerol is also produced as a by-product of betaine production, such as cocoamidopropyl betaine, a surfactant used in industrial cleaners and personal care products.
There exists a need for a system whereby the dehydration of glycerol into acrolein occurs within the liquid phase, and not in the vapor phase. The typical vapor phase dehydration of glycerol requires the use of a water-glycol mixture that must be elevated to a high temperature to form a water vapor along glycerol vapor stream at elevated pressures flowing over a heterogenous, solid acid catalyst bed. The solid acid catalysts are often highly prone to carbonization (carbon fouling) leading to greatly reduced reaction efficiencies due to the blockage of active catalyst reaction sites.
There exists a need for a system whereby acrolein may be added to water systems and dispersed without the danger of the entrainment of air within acrolein storage and feeding systems, and the fire and explosive hazards which would otherwise result.
The present invention meets these needs.